Path selection in optical network for optical nodes with flexible baud rate and modulation format

Abstract

A network controller controls optical nodes configured to communicate with each other at multiple line rates using different tuples of [bits/symbol, symbol rate] for each line rate. The network controller determines multiple paths between two optical nodes, selects a desired line rate at which to communicate between the two optical nodes, and accesses a path database that indicates an available optical bandwidth and an available optical signal-to-noise ratio (SNR) along each path. The network controller determines feasible paths among the paths. To do this, the network controller, for each path, searches the different tuples of the desired line rate for a tuple for which a desired optical bandwidth and a desired optical SNR are accommodated by the available optical bandwidth and the available optical SNR of the path, respectively. The network controller programs optical nodes of one of the feasible paths with a tuple found in the searching.

What is claimed is: 
     
       1. A method comprising:
 at a network controller of a network of optical nodes configured to communicate at multiple line rates using different tuples of [bits/symbol, symbol rate] for each line rate: 
 determining multiple paths between two optical nodes; 
 selecting a desired line rate for the two optical nodes; 
 accessing a path database that indicates available optical bandwidth and available optical signal-to-noise ratio (SNR) referenced to a reference symbol rate along each of the multiple paths; 
 determining one or more feasible paths among the multiple paths by, for each of the multiple paths, searching the different tuples of the desired line rate for a tuple for which a desired optical bandwidth and a desired optical SNR are accommodated by the available optical bandwidth and the available optical SNR of the path, respectively, wherein the searching includes:
 scaling the available optical SNR from the reference symbol rate to the symbol rate of the tuple being searched to produce a scaled optical SNR; and 
 comparing the scaled optical SNR to the desired optical SNR for the tuple being searched; and 
 
 programming optical nodes of one of the feasible paths with a tuple found by the searching. 
 
     
     
       2. The method of  claim 1 , wherein the searching includes searching the different tuples of the desired line rate for a tuple that meets one or more additional conditions imposed on the bits/symbol or the symbol rate. 
     
     
       3. The method of  claim 2 , wherein the searching includes searching for a tuple that has a lowest bits/symbol and corresponding desired optical SNR among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       4. The method of  claim 2 , wherein the searching includes searching for a tuple that has a highest bits/symbol and correspondingly lowest desired optical bandwidth among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       5. The method of  claim 1 , wherein the method further comprises, when the determining one or more feasible paths determines multiple feasible paths:
 for each feasible path of the multiple feasible paths, computing an optical SNR margin as a difference between the available optical SNR for the feasible path and the desired optical SNR for the tuple found for the feasible path; and 
 selecting a feasible path of the multiple feasible paths having a largest optical SNR margin. 
 
     
     
       6. The method of  claim 1 , wherein the path database further indicates a respective time latency for each path, and the method further comprises, when the determining one or more feasible paths determines multiple feasible paths, selecting as the one of the feasible paths a feasible path having a minimum latency among the multiple feasible paths. 
     
     
       7. The method of  claim 1 , wherein the bits/symbol of the different tuples increase across the different tuples, while the symbol rates of the different tuples correspondingly decrease across the different tuples. 
     
     
       8. An apparatus comprising:
 a network interface unit to communicate with a network of optical nodes configured to communicate with each other at multiple line rates using different tuples of [bits/symbol, symbol rate] for each line rate; and 
 a processor coupled to the network interface unit and configured to perform operations including:
 determining multiple paths between two optical nodes; 
 selecting a desired line rate for the two optical nodes; 
 accessing a path database that indicates available optical bandwidth and available optical signal-to-noise ratio (SNR) referenced to a reference symbol rate along each of the multiple paths; 
 determining one or more feasible paths among the multiple by, for each of the multiple paths, searching the different tuples of the desired line rate for a tuple for which a desired optical bandwidth and a desired optical SNR are accommodated by the available optical bandwidth and the available optical SNR of the path, respectively, wherein the searching includes:
 scaling the available optical SNR from the reference symbol rate to the symbol rate of the tuple being searched to produce a scaled optical SNR; and 
 comparing the scaled optical SNR to the desired optical SNR for the tuple being searched; and 
 
 programming optical nodes of one of the feasible paths with a tuple found by the searching. 
 
 
     
     
       9. The apparatus of  claim 8 , wherein the processor is configured to perform the searching by searching the different tuples of the desired line rate for a tuple that meets one or more additional conditions imposed on the bits/symbol or the symbol rate. 
     
     
       10. The apparatus of  claim 9 , wherein the processor is configured to perform the searching by searching for a tuple that has a lowest bits/symbol and corresponding desired optical SNR among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       11. The apparatus of  claim 9 , wherein the processor is configured to perform the searching by searching for a tuple that has a highest bits/symbol and correspondingly lowest desired optical bandwidth among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       12. The apparatus of  claim 8 , wherein the apparatus is further configured to perform, when the determining one or more feasible paths determines multiple feasible paths:
 for each of the multiple feasible paths, computing an optical SNR margin as a difference between the available optical SNR for the feasible path and the desired optical SNR for the tuple found for the feasible path; and 
 selecting a feasible path of the multiple feasible paths having a largest optical SNR margin. 
 
     
     
       13. The apparatus of  claim 8 , wherein the path database further indicates a respective time latency for each path; and
 the processor is further configured to perform, when the determining one or more feasible paths determines multiple feasible paths, selecting as the one of the multiple feasible paths the feasible path having a minimum latency among the feasible paths. 
 
     
     
       14. The apparatus of  claim 8 , wherein the bits/symbol of the different tuples increase across the different tuples, while the symbol rates of the different tuples correspondingly decrease across the different tuples. 
     
     
       15. A method comprising:
 at a network controller of a network of optical nodes configured to communicate at multiple line rates using different tuples of [bits/symbol, symbol rate] for each line rate, wherein the bits/symbol of the different tuples increase across the different tuples, while the symbol rates of the different tuples correspondingly decrease across the different tuples: 
 determining multiple paths between two optical nodes; 
 selecting a desired line rate for the two optical nodes; 
 accessing a path database that indicates an available optical bandwidth and an available optical signal-to-noise ratio (SNR) along each path; 
 determining one or more feasible paths among the multiple paths by, for each path, searching the different tuples of the desired line rate for a tuple for which a desired optical bandwidth and a desired optical SNR are accommodated by the available optical bandwidth and the available optical SNR of the path, respectively; 
 when the determining one or more feasible paths determines multiple feasible paths, selecting a feasible path from the multiple feasible paths based on a predetermined criterion; and 
 programming optical nodes of a selected feasible path with a tuple found by the searching. 
 
     
     
       16. The method of  claim 15 , wherein the selecting the feasible path includes:
 for each of the multiple feasible paths, computing an optical SNR margin as a difference between the available optical SNR for the feasible path and the desired optical SNR for the tuple found by the searching the different tuples for each of the multiple feasible paths; and 
 selecting a feasible path of the multiple feasible paths having a largest optical SNR margin. 
 
     
     
       17. The method of  claim 15 , wherein the path database further indicates a respective time latency for each path, and the selecting includes selecting the feasible paths of the multiple feasible paths having a minimum latency among the feasible paths. 
     
     
       18. The method of  claim 15 , wherein the searching includes searching for a tuple that has a lowest bits/symbol and corresponding desired optical SNR among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       19. The method of  claim 15 , wherein the searching includes searching for a tuple that has a highest bits/symbol and correspondingly lowest desired optical bandwidth among the different tuples and that has a desired optical bandwidth that is able to be allocated in a continuous spectrum of the available optical bandwidth of the path being searched. 
     
     
       20. The method of  claim 15 , wherein the network of optical nodes includes a spectrum switched optical network (SSON) and the optical nodes each includes a reconfigurable optical add-drop multiplexer (ROADM).